It is understood more intimidation and violence has been taking place at the platinum producer’s mine, where 44 people were shot by police last month.
Lonmin, militant union AMCU and other union representatives have been trying to broker a wage deal, and talks are expected to go on throughout the week.
Tensions are expected to be running high as the peace accord, signed at the end of last week, deemed that the workers must return to work for wage demands to be discussed.
The strife at Lonmin, where the majority of its 28,000 workers have not reported for duty, has spread progressively to other mines in the area. On Monday gold producer Gold Fields said 15,000 workers had downed tools and gone on strike.